This invention is generally relative to wireless spread spectrum based multichannel modulation for ultra wideband communications.
On Apr. 22, 2002, U.S. Federal Communications Commission (FCC) released the revision of Part 15 of the Commission's rules regarding ultra-wideband (UWB) transmission systems to permit the marketing and operation of certain types of new products incorporating UWB technology. With appropriate technology, UWB device can operate using spectrum occupied by existing radio service without causing interference, thereby permitting scarce spectrum resources to be used more efficiently. The UWB technology offers significant benefits for Government, public safety, businesses, and consumers under an unlicensed basis of operation spectrum.
UWB device devices can be classified in three types based on the operating restrictions: (1) imaging system including ground penetrating radars and wall, through-wall, surveillance, and medical imaging device, (2) vehicular radar systems, and (3) communications and measurement systems. In general, FCC is adapting unwanted emission limits for UWB devices that are significantly more stringent than those imposed on other Part 15 devices. Limiting the frequency band, which is based on the −10 dB bandwidth of the UWB emission, within certain UWB products will be permitted to operate. For indoor communications and measurement systems, FCC provides a wide variety of UWB devices, such as high-speed home and business networking devices as well as storage tank measurement devices under Part 15 of the Commission's rules subject to certain frequency and power limitations. The indoor UWB devices must operate in the frequency band from 3.1 GHz to 10.6 GHz. UWB communication devices should also satisfy the Part 15.209 limit, which sets the indoor FCC emission limits for UWB system, for the frequency band below 960 MHz and conform the FCC's emission mask for the frequency band above 960 MHz in Table 1:
TABLE 1Frequency (MHz)EIRP (dBm) 0-960−41.3 960-1610−75.31610-1990−53.31990-3100−51.3 3100-10600−41.3Above 10600−51.3
The indoor UWB devices must be designed to ensure that operation can only occur indoor or must consist of hand held devices that may be employed for such activities as peer-to-peer operation. Such UWB devices can be used for wireless communications, particularly for short-range high-speed data transmissions suitable for broadband communication access to networks.
FCC proposed to define an UWB device as any device where the fractional bandwidth is greater than 0.25 based on the formula as follows:
                              FB          =                      2            ⁢                          (                                                                    f                    H                                    -                                      f                    L                                                                                        f                    H                                    +                                      f                    L                                                              )                                      ,                            (        1        )            where fH is the upper frequency of the −10 dB emission point and fL is the lower frequency of the −10 dB emission point. The center frequency of the UWB transmission is defined as the average of the upper and lower −10 dB points as follows:
                              F          C                =                                                            f                H                            +                              f                L                                      2                    .                                    (        2        )            In addition, a minimum frequency bandwidth of 500 MHz must be used for an UWB device regardless of center frequency.
Given an entire frequency bandwidth of 7.5 GHz (3.1-10.6 GHz), it is difficult to design a transmitter and/or receiver device for a single UWB signal that occupies the entire frequency bandwidth from 3.1 GHz to 10.6 GHz directly. This is because we need to have a very-high speed A/D and D/A converter as well as a high-speed circuit and digital signal processor to operate an UWB device for the wireless communications. As a result, the cost of the UWB device could be expense. In addition, interference between the UWB and other devices, such as a WLAN 802.11a device, can occur because the WLAN 802.11a device operates in the lower frequency range from 5.15 GHz to 5.35 GHz or in the upper frequency range from 5.725 GHz to 5.825 GHz. Moreover, the UWB device may not be able to transmit data with scalability.
Due to the proliferation of 7.5 GHz UWB for wireless broadband communications, it would be desirable to have a new technology of developing one multichannel UWB solution, to reduce the interference with the WLAN 802.11a devices and to transmit and receive the transmission data rate with scalability as well as to reduce the cost for indoor UWB devices. Therefore, in this embodiment, the spread spectrum based multichannel modulation is invented for wireless indoor UWB communications.
Thus, there is a continuing need of spread spectrum based multichannel modulation for indoor UWB devices that enable a user to transmit the data rate with scalability and avoid the interference with WLAN 802.11a devices.